Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. In a lithium bromide absorption refrigeration system

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

2. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Piston type reciprocating

Axial

3. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

4.33

3.33

2.33

1.33

4. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Superheated vapour

Dry saturated vapour

Wet vapour

5. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Carnot

Reversed Rankine

6. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(D) Difference of (A) and (B)

(B) Heat stored in the human body

(A) Heat dissipated to the surroundings

7. Most thermostatic expansion valves are set for a superheat of

5°C

20°C

10°C

15°C

8. Rating of a domestic refrigerator is of the order of

0.1 ton

5 tons

10 tons

40 tons

9. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

10. Which of the following cycles uses air as the refrigerant?

Carnot

Ericson

Stirling

Bell Coleman

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11. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 3

9: 1

1: 1

1: 9

12. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

13. Freon group of refrigerants are

Nontoxic and non-inflammable

Toxic

Non-inflammable and toxic

Inflammable

14. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

15. The capillary tube, as an expansion device, is used in

Room air conditioners

Water coolers

All of these

Domestic refrigerators

16. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Normal cooling

Sub-cooling or under-cooling

None of these

17. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

Positive

None of these

Negative

18. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.4

0.6

0.376

0.67

19. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

20. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Less

Unpredictable

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21. The boiling point of ammonia is

-77.7°C

-30°C

-33.3°C

-10.5°C

22. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

High

Low

23. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

24. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

30 bar

2 bar

15 bar

25. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

Above critical temperature

At critical Temperature

Near critical temperature of refrigerant

26. Critical temperature is the temperature above which

Water will evaporate

A gas will never liquefy

A gas will immediately liquefy

Water will never evaporate

27. In a refrigeration system, the expansion device is connected between the

Compressor and condenser

Condenser and receiver

Evaporator and compressor

Receiver and evaporator

28. The value of C.O.P in vapour compression cycle is usually

Equal to unity

Always more than unity

Any one of the above

Always less than unity

29. Which of the following is not a desirable property of a refrigerant?

Good electrical conductor

Large latent heat

High risibility with oil

Low boiling point

30. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₁ / (T₂ - T₁)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

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31. A thermostatic expansion valve in a refrigeration system

Is suitable only for constant load systems

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

32. A bootstrap air cooling system has

Four heat exchangers

Three heat exchangers

One heat exchanger

Two heat exchangers

33. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Superheat the vapour

34. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Evaporator

Absorber

Condenser, absorber and separator (rectifier)

35. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant entropy

Involves no change in volume

Takes place at constant pressure

36. Which of the following statement is correct?

(D) Both (A) and (B)

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

37. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Ammonia

Carbon dioxide

38. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

2.15

1.25

39. The curved lines on a psychrometric chart indicates

Relative humidity

Wet bulb temperature

Dry bulb temperature

Dew point temperature

40. The freezing point of sulphur dioxide is

-135.8°C

-56.6°C

-77.7°C

-75.2°C

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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